1. Field of the Invention
This invention relates to position detecting apparatus having particular utility in self-operating machinery, and more particularly the invention is concerned with a position detecting apparatus which is adapted for use in an operation involving rotating objects of operation, particularly in an operation for mounting wheels onto vehicle hubs in a motor vehicle production line.
2. Description of the Prior Art
In a motor vehicle production line, a wheel mounting operation for mounting wheels onto vehicle hubs and a nut tightening operation for screwing nuts into bolts for fastening the wheels in position after the wheels have been mounted onto the hubs are performed. These operations have hitherto been performed by relying on human brains and labor. These operations will be described more in detail. A wheel is raised by means of a winch or by the hands of the operator and then hub bolts threadably connected to one of the vehicle hubs are inserted into holes formed in the wheel for receiving the hub bolts therein. Thereafter nuts are screwed into the hub bolts as by an impact wrench. In performing the wheel mounting and nut tightening operations, difficulty is encountered for positioning the hub bolts such that they are brought into index with the holes in the wheel for receiving the hub bolts, because the angularly rotated positions of the hub bolts about the axle undergo changes due to the rotation of the hub. Also, when the nuts are tightened on the hub bolts, the operator is subjected to the vibration and noise produced by the impact wrench used to perform the operation. Moreover, the operator must perform the operation of raising the wheel which is heavy, with the result that the operator must bear a heavy burden. Therefore, in order to free the operator from the heavy burden, there has been a demand for automating the wheel mounting operation.
Apparatus designed for automating the wheel mounting operation are disclosed, for example, in the specification of Japanese O.P.I. Publication (laid open to public inspection) No. 78054/75, the specification of Japanese Patent Publication No. 24785/75 and a paper entitled "An Application of Computer Vision to a Simulated Assembly Task" which has been submitted to the First International Joint Conference on Pattern Recognition, 1973, held in Washington, D.C., U.S.A. In performing the operation of mounting wheels on vehicle hubs not only by means of these apparatus but also by other apparatus, the most important problem that is generally encountered is how to carry out positioning of the parts relative to each other for accomplishing the object of assembling or positioning of the hub bolts secured to a hub relative to the holes formed in the wheel for inserting the bolts therein.
The systems for detecting positions in order to accomplish positioning can be broadly divided into a non-contact system and a contact system. The aforementioned three apparatus all belong to the non-contact system. Apparatus of this system have disadvantages in that it is impossible to accomplish positioning with a high degree of precision and that it is impossible to obtain a cycle time which is fit for practical use.